The present invention relates to optical amplifier arrangements and, more specifically, such amplifiers constructed for use in telecommunications systems and/or cable TV systems using broad bandwidths.
Various telecommunications systems have been developed using optical fibers and having a relatively broad bandwidth. Such optical systems have higher channel capacity than wire telecommunications systems. However, the demand for communications channels to carry telephone signals including telephone calls (voice), facsimile, data (such as electronic mail or e-mail), and even video phone calls is growing at a tremendous rate. Some communications systems are envisioned which carry the above telecommunications signals together with cable television signals. The bandwidth of communications systems has limited the channel capacity because such systems often use components with limited bandwidth, introduce noise such as spontaneous emission, and/or are limited to one direction communication (for example, such systems may use amplifiers which can convey and/or amplify signals in only one direction, thus lacking bidirectionality).
Apart from limitations on the channel capacity of communications systems carrying telephone signals and/or cable TV signals, various other problems and constraints are generally present in such communications systems.
A problem with various optical communications systems is a difficulty in providing adequate filtering which will filter out undesired optical signals with a high degree of rejection, while passing a desired optical signal. If one is to use an optical fiber for carrying video or other signals on different wavelengths of laser light, one must have a tuneable optical filter (difficult to achieve satisfactorily) in order to select the wavelength of laser light corresponding to the desired signal or one must have a plurality of dedicated optical filters (each optical filter dedicated to a single wavelength) and an arrangement for selecting from the outputs of the different dedicated optical filters. In either case, complexity, high cost, and other difficulties have generally been encountered.
Communications systems often provide arrangements whereby one can block transmission of a signal such that a local signal can be inserted. For example, if a nationwide cable channel is provided to various local cable TV systems, such local cable TV systems want to be able to insert local commercials. At designated times in the feed from the nationwide cable channel, blocks of time will be provided for the local cable TV company to insert a local commercial. Arrangements for removal and insertion of signals upon a channel are often quite complex and expensive. Such techniques for dropping/inserting signals may require optical filters and thus be subject to the problems noted above with respect to optical filters.
A further problem with various systems is that failure of a single component in a system may cause the system to fail completely. This may result is loss of confidence in the communications system (telephone, cable tv, or both) and cause the provider to loose its customers.
Some components, even components in amplifier systems, in such communications systems may disadvantageously introduce insertion loss.
U.S. Pat. No. 5,283,686, issued Feb. 1, 1994 in the name of the present inventor, entitled OPTICAL SYSTEMS WITH GRATING REFLECTOR, and hereby incorporated by reference discloses amplifier arrangements which avoid or greatly reduce problems with spontaneous emission.